Apply sanitizers to reduce E. coli population.

In the recent past, outbreaks of serious illness caused by E. coli O157:H7 have been associated with apple juice and apple cider. Some of these outbreaks prompted recalls of juice products, as well as an examination by the U.S. FDA of fruit juice processing techniques. The FDA currently requires that packaged fruit juices, including apple cider, which have not been treated to reduce contaminating microorganisms must carry a warning label.

Pasteurization, as a final step in processing cider, can reduce the number of contaminating microorganisms. But heating the product can negatively impact the flavor and appearance of the cider. As an alternative to pasteurization, researchers have examined a variety of ways to reduce bacterial populations, including the use of high pressure and ultraviolet (UV) light.

Scientists at Iowa State University wanted to see if washing whole apples with solutions of three different sanitizers--peroxyacetic acid, chlorine dioxide or a chlorine-phosphate buffer solution--could reduce the levels of a contaminating nonpathogenic E. coli population by 5 logs. They also wanted to determine at what sanitizer concentration and time they could achieve this reduction.

The investigators tested the sanitizers at 1, 2, 4, 8 and 16 times the manufacturers' recommended concentrations at wash times of 5 minutes, 10 minutes and 15 minutes. Whole, sound braeburn apples were inoculated with approximately 1 X [10.sup.8] or 7 X [10.sup.6] colony-forming units (CFUs) per apple. The apples were stored for 24 hours. Then the control was washed with sterile water, and the others with sanitizers for the indicated time.

The investigators enumerated the recovered bacteria on trypticase soy agar. They found that washing the samples with water alone reduced the recoverable population by almost 2 logs from the starting population. This can be attributed to the physical removal of organisms from the apple surface.

No sanitizer, when used at the recommended concentration, was able to reduce the recovered E. coli population by 5 logs under the test conditions. The most effective sanitizer, peroxyacetic acid, achieved a 5-log reduction when used at 2.1 times to 14 times its recommended concentration, depending on the length of wash time.

The chlorine-phosphate buffer solution reduced the population by 5 logs when used at 3 to 15 times its recommended concentration, depending on wash time. The chlorine dioxide did not achieve the 5-log reduction at any concentration or wash time tested. The apples were not visibly altered in appearance or texture after they were treated with the different sanitizers, even at high concentrations.

Further information. Bonita Glatz, Department of Food Science and Human Nutrition, Iowa State University, 2577 Food Sciences Building, Ames, IA 50011; phone: [phone]; fax: [phone]; email: [e-mail].